The invention on hand relates to an abrasive grain, the method production of the grain, and the use of the grain, wherein the grain is provided with a coating of an inorganic or organic binder comprised of aluminum oxide, silicon carbide, cubic boron nitride and/or diamond, and containing abrasive filling materials. The coating contains at least one abrasive substance.
The use of abrasive substances in the production of abradants has been known, and they are frequently used in practice for abradants on a liner (abrasive bands and abrasive papers) as well as for bonded abradants (abrasive disks). The abrasive substances enter into chemical reactions during the grinding or, respectively, cause physical actions that have a positive impact on the grinding process and that lead to an increase of the serviceable life of the tool while simultaneously reducing or completely avoiding any thermal damages to the work piece. Thus, the intended use of the abrasive substances, similar to that of a high-temperature or high-pressure lubricant, is to reduce the friction between the abrasive grain particle and the work piece; to prevent a fusing of the grinding chip with the grain or with the work piece through a reaction with the fresh chip surface; to absorb the heat that is generated in the form of melting, evaporation, sublimation or dissociation heat; and to protect the cutting edges of the abrasive grain particle from any reaction with the material.
Particularly well-suited abrasive substances have turned out to be, e.g., halogenides (chloride of lead, cryolite, fluorite, potassium tetrafluoroborate, et al.); chalcogenides (pyrite, antimony sulfide, zinc sulfide, molybdenum sulfide, et al.); metals with low melting points (Zn, et al.); and high-pressure lubricants (graphite, et al.).
Usually, during the production of the abrasive, the abrasive filling material, in addition to other fillers, is added to the bonding agent mix that is then further processed into the abradant, together with the abrasive grain and other components of the mix (liquid resin, or others). In addition to the abrasive fillers, inactive fillers are frequently used, such as wood or rock dust, chalk, clays et al., that are usually used to fill plastics (for the purpose of saving resins); or compacting fillers, such as, e.g., glass fibers or others, that are used to increase the firmness of the connecting ridge, and/or fillers such as pumice stone or cork powder with the aid of which the self-sharpening properties of an abrasive disk are enhanced.
A disadvantage of this traditional method must be seen in the fact that the abrasive fillers are distributed evenly across the entire abrasive material. However, their abrasive effect is mostly required at a location where the actual abrasive action occurs, to wit: where the abrasive grain collides with the work piece, i.e. in the immediate vicinity of the abrasive grain. Thus, more abrasive fillers are usually used than would be theoretically necessary which is of significance in so far as suitable substances are frequently very expensive and/or toxic.
In German patent publication DE 2 339 507, abrasive wheels are described that are based on abrasive grains featuring a sealing coating with material-active filler properties.
In each of those cases, it involves coatings that must be seen as specific for the production process and for the corresponding abrasive. Thus, the preferred objective is to make it possible to use hygroscopic, subliming or liquid substances as fillers.
Due to the danger of the formation of agglomerates or agglutination, such coated abrasive grains must be processed immediately. They show the same performance, and it is thus possible to reduce the use of abrasive fillers and to make it possible to use new, less critical fillers.